1. Field of the Invention
This invention relates to a battery active material which is useful as, for example, a negative electrode active material in a lithium battery. The invention further relates to a battery using the active material.
2. Description of Related Art
Lithium batteries, owing to their high electromotive force and high energy density, are widely used in information-related devices and communications devices. In the automotive field as well, electric vehicles and hybrid vehicles are being rapidly developed in order to address environmental problems and resource issues, and lithium batteries are under investigation as power supplies for such vehicles. Lithium batteries generally have a positive electrode active material layer containing a positive electrode active material, a negative electrode active material layer containing a negative electrode active material, and an electrolyte layer formed between the positive electrode active material layer and the negative electrode active material layer.
Carbon materials (e.g., graphite) have been used as the negative electrode active material in lithium batteries. On the other hand, active materials having a high thermal stability are desired to further improve battery safety. In this connection, International Patent Application Publication No. 2011/118302 (WO 2011/118302) describes, as a battery active material having a high thermal stability, a battery active material which includes an element M that is a Group III element, the elements titanium (Ti), oxygen (O) and sulfur (S), and contains a M2Ti2O5S2 crystal phase.
To achieve a high battery performance, there exists a desire for a high-capacity battery active material.